Method and apparatus for burning a mixture of liquid and gaseous fuels



Feb. 22, 1966 J. w. BAIN ETAL METHOD AND APPARATUS FR BURNING A MIXTURE OF LIQUID AND GASEOUS FUELS Filed Deo. 19, 1963 2 Sheets-Sheet l fm A II f n IIIH l ulllllllllllllinlllllllll Feb. 22, 1966 1 W, BAIN ETAL 3,236,281

METHOD AND APPARATUS FOR BURNING A MIXTURE OF LIQUID AND GASEOUS FUELS Filed Dec. 19, 1963 2 Sheets-Sheer?l 2 M $.aM n w um ETT mw NW mm Mew I N m V .f J WWW M f N0 A H w mm,

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2S T25 $3995 593m. m95@ ri: Ei E x s- ,L r f hn- QN Nk ,wm Fw m6 United States Patent O 3,236,281 METHGD AND APPARATUS FUR BURNING A MIXTURE F LIQUID AND GASEQUS FUELS John W. Bain, Provo, and Alton E. Sumsion, American Fork, Utah, assignors to United States Steel Corporation, a corporation of Delaware Filed Dec. 19, 1963, Ser. No. 333,260 14 Claims. (Cl. 158-11) This application, which is a continuation-in-part of my cci-pending application, Serial No. 68,430, led November 10, 1960 and now abandoned, relates to a method and apparatus for burning liquid and gaseous fuels, and more particularly for burning such fuels in open hearth furnaces. In burning a combination of gaseous and liquid fuels the common practice is to atomize the liquid fuel, such as tar or oil, by steam at the entry end of the burner and then pass the atomized fuel to the discharge end of the burner. The gaseous fuel may be discharged from the burner around, above or below the atomized liquid fuel. The steam does not add, but rather subtracts sensible heat from the llame, and energy for llame velocity and direction is also wasted by the necessity of driving the emulsion the length of the burner which may be as much as or more than l2 ft. long. The atomizing steam is normally at a pressure of approximately 150 lbs. per sq. in. gauge. The steam also contributes to refractory wear and results in hydrogen pick-up in the molten metal bath, The amount of fuel gas useable with a burner utilizing atomizing steam is also limited.

It has also been suggested to use gas, particularly natural gas, as the atomizing agent. However, to the best of our knowledge when natural gas has been used for this purpose its pressure had to be at least 180 lbs. per sq. in. Since natural gas is not ordinarily available at these pressures it was necessary to compress the natural gas as supplied to the plant. Thus a large investment is required for gas compressors and new piping for the high pressure system. The cost of compressing the gas is also substantial. Also, the atomizer is located at the entry end of the burner, this having Various disadvantages. Also, it is not possible with the suggested equipment to use over 50% of the fuel as natural gas during the .lime boil and relining period and the maximum amount of the fuel requirement or Btu. input from natural gas for the entire heat does not exceed 60%.

It is therefore an object of our invention to provide apparatus for burning liquid and gaseous fuels in which the gaseous fuel, at a relatively low pressure, is used as the atomizing agent for the liquid fuel.

Another object is to provide a burner which is smaller and less expensive than previous burners used for burning a combination of liquid and gaseous fuels.

A further object is to provide such a burner in which oxygen is used.

It is also an object of our invention to provide a method of burning liquid and gaseous fuels in which a higher percentage of natural gas is used than previously.

Still another object is to provide a method of operating an open hearth furnace wherein the hydrogen (from steam) and sulfur (from liquid fuel) pick-up in the molten steel bath from the fuel components is minimized.

A further object is to provide such a method of operating an open hearth furnace in which less limestone, less iluorspar and less fuel is-required.

A still further object is to provide such a method in which the proportion of natural gas used is greater than in prior methods.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURE l is a schematic view of a section of an open hearth furnace showing the location of the burner;

Cil

3,236,281 Patented Feb. 22, 1966 FIGURE 2 is a longitudinal view, partly in section, of a burner of our invention;

FIGURE 3 is an enlarged longitudinal sectional view of the discharge end of the burner of FIGURE 2;

FIGURE 4 is a view taken on the line IV--IV of FIG- URE 3;

FIGURE 5 is a view, partly in section, of they entry end of a modified burner;

FIGURE 6 is a longitudinal sectional view of the discharge end of the burner of FIGURE 5; and

FIGURE 7 is a view taken on the line VII-VII of FIGURE 6.

Referring more particularly to FIGURES 1 to 4 of the drawings, reference numeral 2 indicates an open hearth furnace having dual uptakes 4 at each end thereof, only one of which is shown, and a hearth 6 for supporting the molten metal bath B. A port 8 leads from the uptake 4 to chamber 12. A burner port 14 is located between the section of uptakes 4 and also leads to the chamber 12. Burner 16 is received in the burner port 14 through end wall 18. While the burner is shown illustrated for use in an open hearth furnace and is particularly suitable for that purpose it may be used with other types of furnaces such as boilers and reheating furnaces.

The burner 16 includes a central imperforate tube 20 which in one specific open hearth burner is a l1/2 in. pipe. The entry end of the tube 20 is connected through a reducer 2Q, to a one inch pipe 24 welded to the inside of a Ibushing 26. The tube 20 is unrestricted except at its discharge end. The entry end of the pipe 24 is connected to a source of tar or oil, not shown. The discharge end of the tube 20 is swaged inwardly so as to provide a tapered outer surface 28, which is 'l inch long, and a reduced diameter outlet 3/6 inch in diameter. A second imperforate tube 30 surrounds the central tube 20 in spaced coaxial relationship therewith so as to provide a passageway 32 for receiving gaseous fuel. Spacers 33 insure centering of tube 20 within tube 30. The bushing 26 and the entry end of the tube 3Q are supported in a T 34. The side outlet of T 34 is connected to a source of gaseous fuel having a pressure -of at least 30 lbs. per sq. in. gauge. The tube 3G has a restricted section therein formed by a sleeve 36 welded to the inside of tube 30. The sleeve 316 tapers from a maximum internal diameter on its inlet side lto a minimum internal diameter on its outlet side which is located substantially in the sameA transverse plane as the beginning of sloping portion 28 of tube 20. lIn the specific embodiment of our invention being described the inside diameter of sleeve 36 is 1.40V irrches so as to provide a space .28 inch wide between the sleeve 36 and the outside wall of tube 20. As shown the sleeve 36 is 'I/s inches long. The inside diameter of sleeve 36 and the outside diameter of surface 2S should be such that the area available for discharge of the gaseous fuel toward the liquid fuel must be at least small enough to provide velocity exceeding sonic for the minimum gas tiow and pressure expected without being too small Vto permit maximum flow expected or required. For the burner described the inside diameter of sleeve 36 should not exceed 1.75 and the outside diameter of surface 28 should not be less than 1/2 The upstream end of surface 28 must be veven with or slightly downstream from the downstream end of sleeve 36. It is preferred that the downstream end of surface 28 be a maximum of 1/2 beyond the downstream end of sleeve 36. The distance between the outlet end of tube 20 and the furnace end of the burner is shown' as'71/z inches and should be within l0 of the burner discharge end. A convergent-divergent sleeve 38 is located within the tube 30 between the ends of tubes 2li and 30. As shown, the furnace end of sleeve 38 terminates 3A inch from the end of tube 30 and its minimum internal diameter is 1.50 inches. The sleeves 38, as shown, is 5% inches long with its converging section being 7%; inches long, its throat or flat section 1'1/2 inches long and its divergent se-ction 2% inches long. The convergent portion of sleeve 3-8 should have a steeper pitch than the divergent portion to more nearly approach the shape of a true venturi. It will be seen that the sleeve 38% has a maximum internal d-iameter on its inlet side, tapering to a minimum diameter through a short throat section, and increasing to a maximum internal diameter on its outlet side. The downstream end of sleeve 38 is located anywhere within 3% inches of the discharge end of the burner. The outside of the burner is formed from a 4 inch pipe 40 arranged coaxially with tube 30. The entry end of pipe 40 is received in a T 42 and its furnace end is connected by a closure 44 to tube 30 so as to provide a cooling water chamber 46. A 3 inch pipe 48 is arranged lbetween pipes 30 and 40 and terminates short of the closure 44. The en- -try end of pipe 48 is supported by a T 50 and passes through packing nuts 52 and 54 supported by T 42. T 50 ,supports packing nuts 56 and 58 through which passes tube 30 to T 34. A spider 60, welded to the outside of tube 48, spaces the tube 48 centrally in space 46. Cooling water enters space 46 through the side outlet of T 42, passes forwardly to the furnace endof the space'46 on the voutside of tube 48 land then passes rearwardly on the inside lof tube 48 and discharges Ifrom the side outlet of T 50.

In operation, tar or oil is introduced into tube 20 and passes therethrough with its velocity being increased as it Ais discharged from tube 20 because of the restriction in size of the discharge opening. In one specific embodiment of our invention 200 gallons of tar per hr. are delivered to the entry end of tube 20 under a pressure of 100 lbs.

per sq. in. gauge with the tar leaving the tube 20 at a Velocity of ft. per second. Natural gas is delivered into the side outlet of T 34 under a pressure of at least 30 lbs.

-per sq. in. gauge and is directed inwardly at increased ve- -locity into the tar stream leaving tube 20. The velocity of the gas at the point is at least 1090 ft. per second. In

-one specific embodiment of our invention 115,000 standard cubic ft. of gas per hr. is delivered at 90 lb. gauge pressure .to the tube 30 so 4that the lvelocity at the discharge end of sleeve 36 exceeds 1200 ft. per second and is theoretically 4500 ft. per second. As the gas enters .the fuel stream at sonic Velocity the tar is atomized and the stream of atomized tar and g-as pass through the sleeve 38 where there is an increase in velocity and a decrease in static pressure which further aids in vaporizing the liquid fuel. The location of the sleeve 38 may be varied to change the discharge pattern of the fuel. For proper operation lthe end of the sleeve 38 must be comparatively close to the discharge end of the burner hather than nelarrthe entry end of the burner. I-n the burner shown it is.%" from the discharge end and in all cases must be within 3% from the discharge end. The heat supplied 'by the gas should be at least 30% of the total fuel requirer ment and between 75 and 80% of the B.t.u. input has been provided from the gaseous fuel with good results.

-As the gas liquid fuel mixture leaves the burner the gas -is mixed with the air land immediately burns with an exceedingly brilliant radiant intensity.

In the operation of a steel producing open hearth furnace the maximum amount of fuel is required during the melting period and a lesser amount of fuel is required during the lime boil and refining period. We have found that excellent results are obtained when 20 to 25% of the fuel requirement is furnished by liquid fuel during the major portion of the melting period and the remainder of the fuel requirement furnished as natural gas at a pressure between 3'() and 100 lbs. per sq. in. gauge. During `the lime boil and refining period the ratio of liquid fuel to gaseous `fuel is increased so that from 25 to 30% of the fuel requirement is liquid fuel and the remainder natural gas. During part of the lime boil and refining period the *percentage of natural gas may be lower. By this practice it is possible to utilize up to gaseous fuel for the entire heat.

It is sometimes desirous to add oxygen to the fuel in `the burner. In this embodiment of our invent-ion, which is shown in FIGURES 5 to 7, an imperforate tube 62 is positioned between tubes 20 and 30 and a T 64 is attached to the inlet end thereof adjacent the T 34. The tube 20 is centered within the tube 62 by means orf spacers 66 and extends into the T 64. A reducer 68, pipe 70 and T 72 are attached to the entry end of tube 20. Liquid fuel is provided through one run of the T 72 and purge steam through the side outlet of T 72. The construction is other- Wise the same as in the first embodiment and the same reference numerals are used to indicate like parts. In this arrangement the tube 30 may be a 2" pipe, the tube 62 a 5X1 pipe and the tube 20 a 1% pipe. The velocity of the liquid fuel and the gaseous fuel is substantially the same as in the first embodiment. The velocity of the oxygen will vary with Variation in flow but must exceed sonic velocity. When the burner is on idle cycle during open hearth furnace operation purge steam will be introduced through T 72.

While several embodiments of our invention have been shown in described it will be apparent that other adaptations and modificati-ons may be made without departing from the scope of the following claims.

We claim:

1. Apparatus for burning a mixture of liquid and gaseous fuels comprising a central tube having an imperforate wall and an inlet end adapted to be connected to a source of liquid fuel and an outlet end of reduced internal diameter, said tube having a discharge opening at its outlet end, the outer surface of "the tube adjacent said outlet end tapering inwardly from a maximum diameter to a minimum diameter at the discharge opening, a second tube having an imperforate wall surrounding said central tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of gaseous fuel and an outlet end extending a substantial distance beyond the outlet end of said central tube, said second tube having a passage with means forming a restriction therein tapering from a maximum diameter on the inlet side to a minimum diameter at a transverse plane approximately through that end of the tapered surface on said central tube remote from said discharge opening, said restriction directing said gaseous fuel inwardly at increased velocity into the liquid fuel to atomize the latter, and an imperforate oxygen tube within said second tube surrounding said central tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of oxygen and an outlet end terminating adjacent sai-d transverse plane, said oxygen tube being spaced from said second tube to provide a fuel gas passageway.

2. Apparatus for burning a mixture of liquid and gaseous fuels comprising a central tube having an imperforate wall and an inlet end adapted to be connected to a source of liquid fuel and an outlet end of reduced internal diameter, said tube having a discharge opening at its outlet end, the outer surface of the tube adjacent said outlet end tapering inwardly from a maximum diameter to a minimum diameter at the discharge opening, a second tube having an imperforate wall surrounding said central tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of gaseous fuel and an outlet end extending a substantial distance beyond the outlet end of said central tube, said second tube having a passage with means forming a restriction therein tapering from a maximum diameter on the inlet side to a minimum diameter at a transverse plane approximately through that end of the tapered surface on said central vtube remote from said discharge opening, said restriction of second tube and the outlet end of said central tube said portion gradually decreasing to a minimum internal diameter and then gradually increasing to a maximum internal diameter adjacent the outlet end of said second tube, and an imperforate oxygen tube within said second tube surrounding said central tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of oxygen and an outlet end terminating adjacent said transverse plane, said oxygen tube being spaced from said second tube to provide a fuel gas passageway.

3. Apparatus for burning a mixture of liquid and gaseous fuels according to claim 2 including a third tube in spaced coaxial relaitonship with said second tube to provide a cool-ing water chamber.

4. Apparatus for burning a mixture of liquid and gaseous fuels comprising a straight unobstructed central tube of substantial length having an imperforate wall and an inlet end adapted to be connected to a source of liquid fuel and an outlet end of reduced internal diameter, said tube having a discharge opening at its outlet end, the outer surface of the tube adjacent said outlet end tapering inwardly from a maximum diameter to a minimum diameter at the discharge opening, a second straight tube surrounding said central tube over the majority of its length and in spaced coaxial relationship therewith, said second tube having an imperforate wall, an inlet end adapted to be connected to a source of gaseous fuel and an outlet end extending a substantial distance beyond the outlet end of said central tube, said second tube having a passage with means forming a restriction therein tapering from a maximum diameter on the -inlet side to a minimum diameter at a transverse plane approximately through that end of the tapered surface on said central tube remote from said discharge opening, said restriction directing said gaseous fuel inwardly at increased velocity into the liquid fuel to atom-ize the latter, the minimum diameter of said restriction being greater than the outer diameter of said central tube, said passage including means forming a portion between the outlet end of second tube and the outlet end of said central tube said portion gradually decreasing to a minimum internal diameter and then gradually increasing to a maximum internal diameter at a position within 3%; in. of the outlet end of said second tube, the distance between the outlet ends of said central and second tubes being a maximum of l0 inches and substantially less than the length of said central tube, a third tube in spaced coaxial relationship with said second tube to provide a cooling water chamber, and an imperforate oxygen tube within said second tube surrounding said central tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of oxygen and an outlet end terminating adjacent said transverse plane, said oxygen 4tube being spaced from said second tube to provide a fuel gas passageway.

5. The method of burning liquid and gaseous fuels by a burner having an inner tube with a discharge end surrounded by a coaxial outer tube with a discharge end, said outer tube having its discharge end extending beyond the discharge end of said inner tube, which method comprises passing liquid fuel through the inner tube and discharging it at increased velocity from the discharge end thereof, passing gaseous fuel between the inner and outer tubes and directing it inwardly at increased velocity around the discharge end of said inner tube, the directed gaseous feul stream having supersonic velocity which is greater than the liquid fuel velocity so as to atomize said liquid fuel, liowing said gaseous and liquid fuels through said outer tube to the discharge end thereof, and delivering oxygen at supersonic velocity between the discharged liquid fuel and the gaseous fuel.

6. The method of burning liquid 4and gaseous fuels by a burner having an inner tube with a discharge end surrounded by a coaxial outer tube with a discharge end, said outer tube having its discharge end extending beyond the discharge end of said inner tube, which method comprises passing liquid fuel through the inner tube and discharging it at increased velocity from the discharge end thereof, passing gaseous fuel between the inner and outer tubes and directing it inwardly at increased velocity around the discharge en-d of said inner tube, the directed gaseous fuel stream having supersonic velocity which is greater than the liquid fuel velocity so as to atomize said liquid fuel, owing .said gaseous and liquid fuels through a convergent-divergent passage in said outer tube to the discharge end thereof, and delivering oxygen at supersonic velocity between the `discharged liquid fuel and the gaseous fuel.

7. The method of operating an open hearth furnace which comprises supplying a maximum of 70% of the fuel requirement as liquid fuel through a tube, increasing the velocity of said liquid fuel as it leaves said tube, supplying a minimum of 30% of the fue-l requirement as gaseous fuel through a second tube and discharging it at supersonic velocity into said liquid fuel to .atomize the same, discharging said atomized fuel Amixture into combustion ai-r, burning said fuels in said furnace, and delivering oxygen .at supersonic velocity between the discharged liquid fuel and the gaseous fuel.

8. The method of operating an open hearth furnace which comprises supplying a maximum of 70% of the fuel requirement as liquid fuel through an inner tube, increasing the velocity of lsaid liquid fuel as it leaves said tube, supplying a minimum of 30% of the fuel requirement as gaseous fuel through an outer second tube having a discharge end and `discharging it at supersonic velocity into said liquid fuel to atomize the same, flowing said gaseous and liquid fuels through a convergentdivergent passage in said outer tube to the discharge end thereof, discharging said atomized fuel mixture into combustion air, burning said fuels in said furnace, and delivering oxygen at supersonic velocity between the discharged liquid fuel and the gaseous fuel.

9. The method of operating a steel producing open hearth furnace which comprises supplying from 20 to 25% of the 4fuel requirement as liquid fuel through a tube during the major portion of the melting period, increasing the velocity of said liquid fuel as it leaves said tube, supplying the remainder of the fuel requirement as gaseous fuel at a maximum pressure of 100 lbs. :per sq. in. gauge and discharging it at supersonic velocity into said liquid lfuel to atomize the same, discharging said atomized fuel mixture into combustion air, burning said fuels in said furnace, increasing the ratio of liquid fuel to gaseous fuel during the lime boil and refining period so that from 25% to 30% of the fuel requirement is liquid fuel yat least a part of the time, and delivering oxygen at supersonic velocity between the discharged liquid fuel and the gaseous fuel.

1d. Apparatus for burning a mixture of liquid and gaseous fuels comprising a central tube having an imperforate wall and an inlet end adapted to be connected to a source of liquid fuel and an outlet end of reduced internal diameter, said tube having a discharge opening at its outlet end, the outer surface of the tube adjacent said outlet end tapering inwardly from a maximum diameter to a minimum diameter at the discharge opening, and a second tube having an -imperforate wall surrounding said lcentral tube in spaced coaxial relationship therewith and having an inlet end adapted to be connected to a source of gaseous fuel and an outlet end extending a substantial distance beyond the outlet end of said central tube, said second tube having a longitudinal passage With lmeans forming a restriction therein tapering from a maximum diameter on the inlet side to a minimum diameter at a transverse plane approximately through that end of the tapered surface on said central tube remote from said discharge opening, the internal diameter of said passage returning to its maximum immediately after said restriction, the portion of said central tube within said restriction having a substantially uniform outside diameter, said restriction directing said gaseous fuel inwardly Iat increased velocity yinto the liquid fuel to atomize the latter, ysaid passage including means forming a port-ion a substantial distance beyond the outlet end of said central tube gradually decreasing to a minimum internal diameter and then gradually increasing to a maximum internal diameter adjacent the outlet end of said second tube.

11. Apparatus for burning a mixture lof liquid and gaseous fuels comprising a straight unobstructed central tube of substantial length having an imperforate wall and an inlet end adapted to be connected to a source of liquid fuel and an outlet end of reduced internal diameter, said tube having a discharge opening at its outlet end, the outer surface of the tube adjacent said outlet end tapering inwardly from a maximum diameter to a minimum diameter at the discharge opening, a second straight tube surrounding -said central tube over the majority of its length and in spaced coaxial relationship therewith, said second tube having an imperforate wall, an inlet end adapted to `be connected to a source of gaseous fuel and an outlet end extending a substantial distance beyond the 'outlet end of said central tube, said second tube having a longitudinal passage with means forming a restriction therein tapering from a maximum diameter on the inlet side to a minimum diameter at a transverse plane approximately through that end of the tapered surface on said central tube remote from said discharge opening, the internal diameter of said passage returning to its maximum immediately after said restriction, the portion of said central tube within said restriction having a substantially uniform outside diameter, said restriction directing said gaseous fuel inwardly at increased velocity into the liquid fuel to atomize the latter, the minimum diameter of said restriction being greater than the outer diameter of said central tube, said passage including means forming a portion a substantial distance beyond the outlet end of said central tube gradually decreasing to a minimum internal diameter and then gradually increasing to a maximum internal diameter at a position Within 3% in. of the outlet end of said second tube, the distance between the outlet ends of said central and second tubes being a maximum of 10 inches and substantially less than the length of said central tube, .and a third tube in spaced coaxial relationship with said second tube to provide a cooling water chamber.

12. The method of burning liquid and gaseous fuels by a burner having an inner tube with a discharge end surrounded by a coaxial outer tube with a discharge end, said outer tube having its discharge end extending beyond the discharge end of said inner tube, which method comprises passing liquid fuel through the inner tube, increasing the velocity of said liquid fuel adjacent the discharge end of the inner tube and discharging it at the increased velocity from the discharge end thereof, passing gaseous fuel between the inner and outer tubes at a high velocity and directing and accelerating it inwardly at a still higher velocity around the discharge end of said inner tube, the directed gaseous fuel stream being accelerated to at least a supersonic velocity which is greater than the liquid fuel velocity so as to atomize said liquid fuel, and owing said gaseous and liquid fuels through a substantially uniform diameter passage of said outer tube and then through a convergent-divergent passage in said outer tube to the discharge end thereof.

13. The method of claim 12 in which the atomized fuel is discharged into combustion air and burned in an open hearth furnace, and the liquid fuel provides a maximum of of the fuel requirement and the gaseous fuel provides a minimum of 30% of the fuel requirement.

14. The method of claim 13 which includes supplying from 20 to 25% of the fuel requirement as liquid fuel during the major portion of the melting period, and increasing the ratio of liquid fuel to gaseous fuel during the lime boil and rening period so that from 25 to 30% of the fuel requirement is liquid fuel at least a part of this time.

References Cited by the Examiner UNITED STATES PATENTS Re. 23,372 6/1951 Crowe 158-1l 1,441,915 l/1923 Ellis et al 158-76 1,688,320 10/1928 Bassett 158-76 1,983,927 12/1934 Bent et al. 158-11 X 3,000,435 9/1961 Bloom 158-11 OTHER REFERENCES Power: How About Atomizing Oil With Natural Gas (Thompson), published by McGraw-Hill, August 1958; vol. 102, page S.

FREDERICK L. MATTESON, IR., Primary Examiner.

MEYER PERLIN, JAMES W. WESTHAVER,

Examiners. 

1. APPARATUS FOR BURNING A MIXTURE OF IQUID AND GASEOUS FUELS COMPRISING A CENTRAL TUBE HAVING AN IMPERFORATE WALL AND AN INLET END ADAPTED TO BE CONNECTED TO A SOURCE OF LIQUID FUEL AND AN OUTLET END OF REDUCED INTERNAL DIAMETER, SAID TUBE HAVING A DISCHARGE OPENING AT ITS OUTLET END, THE OUTER SURFACE OF THE TUBE ADJACENT SAID OUTLET END TAPERING INWARDLY FROM A MAXIMUM DIAMETER TO A MINIMUM DIAMETER AT THE DISCHARGE OPENING, A SECOND TUBE HAVING AN IMPERFORATE WALL SURROUNDING SAID CENTRAL TUBE IN SPACED COAXIAL RELATIONSHIP THEREWITH AND HAVING AN INLET END ADAPTED TO BE CONNECTED TO A SOURCE OF GASEOUS FUEL AND AN OUTLET END EXTENDING A SUBSTANTIAL DISTANCE BEYOND THE OUTLET END OF SAID CENTRAL TUBE, SAID SECOND TUBE HAVING A PASSAGE WITH MEANS FORMING A RESTRICTION THEREIN TAPERING FROM A MAXIMUM DIAMETER ON THE INLET SIDE TO A MINIMUM DIAMETER AT A TRANSVERSE PLANE APPROXIMATELY THROUGH THAT END OF THE TAPERED SURFACE ON SAID CENTRAL TUBE REMOTE FROM SAID DISCHARGE OPENING, SAID RESTRICTION DIRECTING SAID GASEOUS FUEL INWARDLY AT INCREASED VELOCITY INTO THE LIQUID FUEL TO ATOMIZE THE LATTER, AND AN IMPERFORATE OXYGEN TUBE WITHIN SAID SECOND TUBE SURROUNDING SAID CENTRAL TUBE IN SPACED COAXIAL RELATIONSHIP THEREWITH AND HAVING AN INLET END ADAPTED TO BE CONNECTED TO A SOURCE OF OXYGEN AND AN OULET END TERMINATING ADJACENT SAID TRANSVERSE PLANE, SAID OXYGEN TUBE BEING SPACED FROM SAID SECOND TUBE TO PROVIDE A FUEL GAS PASSAGEWAY. 